Ib Diamond Research Articles

Investigating the broom-like inclusions in type Ib diamond single crystal synthesized by high pressure high temperature

The exceptional properties of diamonds enable diverse applications. However, the applications are significantly hindered by its inclusions. In this study, a specific type of inclusion, broom-like inclusions, has been investigated. The broom-like inclusions in diamonds were synthesized through various high-pressure high-temperature (HPHT) experiments. The synthesis methods were optimized by adjusting the metal catalyst composition, synthesis temperature, Mg(OH)2 content, and nitrogen getter (Ti). The broom-like inclusion morphology and composition were physically characterized and analyzed using various methods. Optical microscopy and SEM were utilized to characterize the morphology and shape of the inclusions, while Raman spectroscopy and Fourier Transform Infrared Spectroscopy were employed to analyze the influence of the defects on the properties of diamonds and investigate the composition of the broom-like inclusions. Gaseous inclusions emerged as crucial for broom-like inclusion formation. They probably originated from residual gases like H2 and CH4. The investigation of broom-like inclusions within diamond crystals has led to the development of various synthetic methods for producing inclusion-free crystals. The findings of this study offer valuable insights into the nature and origin of these inclusions in diamonds, as well as provide strategies to mitigate their formation during production.

Vertical Schottky diode on (113) oriented homoepitaxial diamond

Vertical Schottky diodes were fabricated on (113) oriented diamond substrates produced from thick heavily boron doped (NA ∼ 3.5 × 1020 cm−3) diamond layers grown on HPHT-grown synthetic Ib diamond crystals. The p+-substrates were overgrown by a low doped p-epilayer whose surface layer was compensated up to the depth of 0.1 to 0.3 μm. The surface was then oxygen terminated and covered by evaporated Mo/Au Schottky contacts. The bottom ohmic contact to p+-substrate was formed by Ti/Au bi-layer. Current- and capacitance-voltage characteristics of the realized diodes were measured at temperatures ranging from 25 to 180 °C. At room temperature, the realized diodes show high forward current densities JF = 100 A/cm2 and low differential ON-state specific resistance Ron_sp = 3.7 mΩ.cm2 at forward voltage VF = 4 V and a very low leakage (JR < 10−9 A/cm2) in the blocking regime. At 180 °C, forward characteristics significantly improve (JF = 5 kA/cm2, Ron_sp = 0.2 mΩ.cm2 at VF = 4 V) while the blocking characteristics remain almost unchanged (JR = 6 × 10−8 A/cm2 at VR = 4 V). The breakdown electric field is about 3 MV/cm and the rectification ratio keeps at the level of 1011. Characteristics of realized diodes, which are fully comparable to those of Schottky-pn diodes prepared on (111) oriented boron doped diamond, confirm the suitability of (113) orientation for realization of vertical diamond power devices.

The characterization of diamond single crystal growing along (100) after annealing treatment under high pressure and high temperature

Diamond has many desirable properties. In this study, temperature gradient method was used to prepare a series of type Ib diamond single crystals, which were processed again to obtain and characterize Type IaA diamonds with even more desirable properties. Before annealing, Fourier-transformed infra-red(FTIR) spectra of diamond showed peaks at 1130 cm−1 and 1344 cm−1; After annealing, the peak at 1282 cm−1 was appeared in FTIR spectra of diamonds This data indicated that the isolated nitrogen in diamond aggregated after high-pressure and high-temperature (HPHT) method annealing experiment. Moreover, photoluminescence (PL) spectra suggested that no nitrogen-related color centers existed in the diamond before annealing. In contrast, after annealing, a peak at 637 nm appeared in the PL spectra, indicating the appearance of NV−colors centers type Ib diamond post-annealing. The experimental results show that type Ib diamond crystals can be decolorized after 60 min of annealing under 7 GPa and 1850 °C, which makes part of the area transparent. Under 7 GPa and 2100 °C, type Ib diamond crystals can produce NV color center when annealed for 3 min. With increasing annealing temperature and prolonged annealing duration, the density and size of etch pits on the crystal surface escalated. Therefore, this study provides a guideline for the decolorization of diamonds by HPHT annealing. Moreover, this study also reports a method to change the crystal type and obtain NV color centers under ultra-high-temperature annealing conditions of 7 GPa pressure and 2100 °C temperature, which can be applied to develop quantum materials.

Study on the synergistic mechanism of N[sbnd]H[sbnd]S[sbnd]O co-doping in diamonds

Nitrogen impurity remains a crucial focus in diamond impurity research. To address difficulties associated with excessive nitrogen impurities during the synthesis of high-quality diamonds under high-pressure and high-temperature conditions and to increase the proportion of aggregated nitrogen impurities in diamonds, we explored the multi-element growth environment of natural diamonds. In this study, we used N–H–S–O multi-component co-doping to increase the proportion of aggregated nitrogen impurities in diamond. Through Fourier-transform infrared spectroscopy characterization, we successfully used the synergistic mechanism of N–H–S–O co-doping to achieve a 47.9% proportion of aggregated nitrogen impurities in diamond in a single synthesis and successfully synthesized the type IaA + Ib diamond. Raman tests revealed a lower residual stress in the high-quality large single-crystal diamond synthesized. Moreover, we comprehensively analyzed the mechanism of N–H–S–O co-doping to increase the proportion of nitrogen impurities in diamond aggregates and proposed an optimal ratio principle based on the experimental results. This study presents a method for synthesizing diamonds with a high proportion of aggregated nitrogen impurities and provides valuable guidance for elucidating the origin of natural diamonds and synthesizing multi-doped functional diamonds.

Direct Multiphoton Femtosecond Infrared Laser Excitation of a Diamond Lattice in the Two-Phonon Region and Modification of Color Centers

The nonlinear absorption of ultrashort laser pulses with intensities of 0.17–1.7 TW/cm2 at an intrinsic two-photon absorption wavelength of 4673 nm in type IIb diamond has been studied experimentally. It has been shown that the main absorption mechanism in the studied sample is two-photon absorption with a coefficient of β2 = (72 ± 7) cm/TW. Transmission microspectroscopy, visible photoluminescence, and infrared Fourier-transform microspectroscopy have demonstrated the possibility of laser-induced transformation of nitrogen impurity centers in synthetic type Ib diamond at higher radiation intensities.

Hydrogen-related defects in diamond: A comparison between observed and calculated FTIR spectra

A comprehensive and up-to-date compilation of observed and calculated hydrogen (H)-related peaks that occur in the near- and middle-infrared spectra of diamond is presented. The experimental database contains >300 observed peaks attributed to H-related impurities in natural diamond. The database of calculated peaks includes data from first-principles simulations of the FTIR spectra of different VxNyHz defects in diamond and contains >300 peaks that correspond to different C-H, N-H, and B-H vibrational modes for each VxNyHz defect. Less than ~10 % of observed H-related peaks have been assigned to specific defects. Consequently, the computational database was constructed to better understand the properties of different VxNyHz defects that may correspond to different observed peaks. In general, hydrogen-rich diamonds with a dominant Type Ib character and thus poorly aggregated N, show a larger number of low-intensity, H-related peaks compared to diamonds with a dominant Type Ia character. For example, ~51 % of observed H-related peaks are only observed in Type Ib diamonds, ~9 % of peaks are only observed in diamonds with a dominant Type Ia character and ~40 % of peaks are observed in both Type Ia and Type Ib diamonds. There is a major increase in the number of distinct H-related peaks in Type IaA + Ib diamonds compared to Type Ib diamonds suggesting N-aggregation processes responsible for the formation of A-centers may also produce many distinct VxNyHz defects capable of trapping H. There is a major decrease in the number of H-related peaks in Type IaA > Ib diamonds compared to Type IaA + Ib diamonds suggesting that many of the VxNyHz defects associated with the initial production of A-centers become unstable with increasing mantle residence time and the progressive loss of C-centers. These defects likely combine (or disaggregate and then re-combine) to form fewer, relatively more intense, H-related peaks observed in Type IaA > Ib diamonds. Many of these peaks persist through continued annealing in the mantle and are observed in Type IaA, IaAB, and IaB diamonds. Our data suggests that N and H incorporation are not correlated during diamond growth and that in the early stages of diamond residence, H is incorporated into many distinct VxNyHz defects that involve C- and A-centers. With continued residence and annealing, and the progressive formation A-centers and loss of C-centers, these defects aggregate to form relatively fewer, presumably more stable, VxNyHz defects such as VN3H.

P1 Center Electron Spin Clusters Are Prevalent in Type Ib Diamonds.

Understanding the spatial distribution of the P1 centers is crucial for diamond-based sensors and quantum devices. P1 centers serve as polarization sources for dynamic nuclear polarization (DNP) quantum sensing and play a significant role in the relaxation of nitrogen vacancy (NV) centers. Additionally, the distribution of NV centers correlates with the distribution of P1 centers, as NV centers are formed through the conversion of P1 centers. We utilized DNP and pulsed electron paramagnetic resonance (EPR) techniques that revealed strong clustering of a significant population of P1 centers that exhibit exchange coupling and produce asymmetric line shapes. The 13C DNP frequency profile at a high magnetic field revealed a pattern that requires an asymmetric EPR line shape of the P1 clusters with electron-electron (e-e) coupling strengths exceeding the 13C nuclear Larmor frequency. EPR and DNP characterization at high magnetic fields was necessary to resolve energy contributions from different e-e couplings. We employed a two-frequency pump-probe pulsed electron double resonance technique to show cross-talk between the isolated and clustered P1 centers. This finding implies that the clustered P1 centers affect all of the P1 populations. Direct observation of clustered P1 centers and their asymmetric line shape offers a novel and crucial insight into understanding magnetic noise sources for quantum information applications of diamonds and for designing diamond-based polarizing agents with optimized DNP efficiency for 13C and other nuclear spins of analytes. We propose that room temperature 13C DNP at a high field, achievable through straightforward modifications to existing solution-state NMR systems, is a potent tool for evaluating and controlling diamond defects.

On the creation of near-surface nitrogen-vacancy centre ensembles by implantation of type Ib diamond

Dense, near-surface (within ∼10\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sim 10$$\\end{document} nm) ensembles of nitrogen-vacancy (NV) centres in diamond are moving into prominence as the workhorse of many envisaged applications, from the imaging of fast-fluctuating magnetic signals to enacting nuclear hyperpolarisation. Unlike their bulk counterparts, near-surface ensembles suffer from charge stability issues and reduced formation efficiency due to proximity to the diamond surface. Here we examine the prospects for creating such ensembles by implanting nitrogen-rich type Ib diamond, aiming to exploit the high bulk nitrogen density to combat surface-induced band bending. This approach has previously been successful at creating deeper ensembles, however we find that in the near-surface regime there are fewer benefits over nitrogen implantation into pure diamond substrates. Our results suggest that control over diamond surface termination during annealing is key to successfully creating high-yield near-surface NV ensembles generally and implantation into type Ib diamond may be worth revisiting once that has been accomplished.Graphical

HTHP synthesis and characterization of 5–8 mm diamond large crystal by Fe-Co alloy catalyst

IIa-type diamonds with 5–8 mm edge lengths were successfully synthesized under the catalytic action of Fe-Co catalyst. The effects of Fe-Co and Fe-Ni catalysts on the synthesis of type Ib diamonds were compared and analyzed. Moreover, the effects of different levels of nitrogen-getter agents on the synthesis of type IIa diamonds were discussed. When we characterized the single diamond crystals, Optical microscopy, Raman spectroscopy, Fourier infrared absorption spectroscopy, and photoluminescence spectroscopy were used. The experimental results showed that the nitrogen content of the diamonds synthesized using Fe-Co alloy catalyst was reduced by 127 ppm compared with those synthesized using Fe-Ni alloy catalyst. When the amount of nitrogen-getter added was increased from 0.4 wt% Ti + 0.5 wt% Cu to 0.7 wt% Ti + 0.8 wt% Cu in the Fe-Co-C system, the nitrogen content in the diamond was reduced from 20 ppm to 1 ppm, the internal crystal stress decreased from 238.1 MPa to 147.4 MPa, and the crystal quality was significantly improved. In addition, the Fe-Co alloy catalysts have a lower V-shaped growth zone of diamond, so its growth region is closer to the graphite-diamond equilibrium line, resulting in slower crystal growth and less impurity content in the crystal. Thus, Fe-Co alloy catalysts can synthesize gem-quality diamonds more easily.

Studies of Dislocations in Type Ib, Type IIa HPHT and CVD Single Crystal Diamonds

In this review, the X-ray topography results of various types of single crystal diamonds (SCDs) are reported. Dislocations and dislocation bundles are present in all types of SCDs, the only exception being type IIa high-pressure, high-temperature (HPHT) SCDs. The technology of growing HPHT type IIa SCDs has advanced to a level where the samples show almost no dislocations or dislocation bundles. However, very few groups appear to have perfected the process of HPHT growth of type IIa SCDs. There appears to be a characteristic difference in the dislocations present in type Ib HPHT and chemical vapor deposited (CVD) SCDs. The dislocations in CVD SCDs are mostly in aggregate form, while in HPHT type Ib diamonds there are line dislocations which propagate in &lt;111&gt; or &lt;112&gt; directions. The CVD SCDs growth appears to be in the early stage in terms of the control of dislocations and dislocation bundles, compared to other semiconductor wafers. The dislocations and dislocation bundles and aggregates in SCDs limit their applications in electronic and optical devices. For instance, high-power laser windows must have low dislocations and dislocation bundles. For electronic devices such as high-power diodes, dislocations reduce the breakdown voltage of SCDs, limiting their applications. The knowledge of dislocations, their identification and their origin are, therefore, of utmost importance for the applications of SCDs, be they HPHT or CVD grown.

Large Room Temperature Bulk DNP of 13C via P1 Centers in Diamond.

We use microwave-induced dynamic nuclear polarization (DNP) of the substitutional nitrogen defects (P1 centers) in diamond to hyperpolarize bulk 13C nuclei in both single crystal and powder samples at room temperature at 3.34 T. The large (>100-fold) enhancements demonstrated correspond to a greater than 10 000-fold improvement in terms of signal averaging of the 1% abundant 13C spins. The DNP was performed using low-power solid state sources under static (nonspinning) conditions. The DNP spectrum (DNP enhancement as a function of microwave frequency) of diamond powder shows features that broadly correlate with the EPR spectrum. A well-defined negative Overhauser peak and two solid effect peaks are observed for the central (mI = 0) manifold of the 14N spins. Previous low temperature measurements in diamond had measured a positive Overhauser enhancement in this manifold. Frequency-chirped millimeter-wave excitation of the electron spins is seen to significantly improve the enhancements for the two outer nuclear spin manifolds (mI = ±1) and to blur some of the sharper features associated with the central manifold. The outer lines are best fit using a combination of the cross effect and the truncated cross effect, which is known to mimic features of an Overhauser effect. Similar features are also observed in experiments on single crystal samples. The observation of all of these mechanisms in a single material system under the same experimental conditions is likely due to the significant heterogeneity of the high pressure, high temperature (HPHT) type Ib diamond samples used. Large room temperature DNP enhancements at fields above a few tesla enable spectroscopic studies with better chemical shift resolution under ambient conditions.

Spectroscopic Study of the 3107 cm−1 and 3143 cm−1 H-Related Defects in Type Ib Diamonds

Hydrogen-related infrared absorption bands in natural diamonds have been extensively investigated and widely used to identify natural, treated, and synthetic diamonds grown by high pressure and high temperature (HPHT) and chemical vapor deposition (CVD) techniques. However, the evolutional behavior of the hydrogen-related defects and the relationship between the hydrogen-related and nitrogen-related defects in natural and HPHT-treated Ib diamonds are unclear. In this article, the hydrogen-related defects, particularly the infrared absorption bands of 3107 cm−1 and 3143 cm−1 in natural type Ib diamonds and HPHT-treated natural diamonds, were systematically investigated using spectroscopic techniques. It was found that the 1405 cm−1 absorption intensity was directly proportional to the 3107 cm−1 absorption intensity; the 3143 cm−1 absorption intensity increased with the increase in the 3107 cm−1 absorption intensity, but there was no strict linear relationship between them. The 3143 cm−1 band was not only related to the intensity of the 3107 cm−1 but also related to the value of NC/NA in natural diamonds. When the value of NC/NA was less than one, the 3143 cm−1 band was more pronounced. After high-temperature annealing, the absorption intensities of the 3107 cm−1 and 3143 cm−1 in natural type Ib diamonds became stronger. However, in HPHT synthetic diamonds, only a 3107 cm−1 defect was introduced with the increase in the A centers in the diamonds. The difference and the detectability of the 3143 cm−1 and 3107 cm−1 bands investigated could be efficiently used to identify natural type Ib diamonds from their counterparts, including the synthetic diamonds and the HPHT-treated diamonds.

Quasi-vertical diamond temperature sensor by using Schottky–pn junction structure diode

A Schottky–pn junction structure diode (SPND) has been fabricated on HPHT Ib (001) diamond substrate for temperature sensor application. The forward current-voltage characteristics show an obvious temperature dependency with the turn-on voltages decrease with the increasing temperature. It demonstrates that three types of current transport mechanisms are found at different forward bias voltages. Furthermore, based on the good linear relationship between the turn-on voltages and temperatures, the sensing ability is evaluated at the sub-threshold region. At low current densities (<10−2 A/cm2) high thermal sensitivities are reached (>4.75 mV/K, with a maximum value of 5.31 mV/K at 10−3 A/cm2 of current density) which is remarkably above the sensitivity obtained by other semiconducting material devices. Furthermore, the deviation of sensitivity from the theoretic model is attributed to the relatively higher ideality factor value.

Electron irradiation-induced paramagnetic and fluorescent defects in type Ib high pressure–high temperature microcrystalline diamonds and their evolution upon annealing

Defects introduced to synthetic type Ib diamond micrometer-size particles by electron-beam irradiation were studied by electron paramagnetic resonance and photoluminescence (PL) spectroscopy as a function of e-beam fluence and post-irradiation thermal annealing. Increasing electron-beam fluence causes a substantial reduction of the substitutional nitrogen (P1) content, accompanied by progressively higher concentrations of paramagnetic negatively charged vacancies (V−) and triplet interstitials (R1/R2). Annealing results in a drastic decrease in the V− and R1/R2 content and an increase in the negatively charged nitrogen-vacancies (NV− or W15). Analysis of PL spectra allows for identification of color centers in the irradiated diamond samples and following their evolution after annealing. These data facilitate understanding of different factors contributing to the formation of color centers in diamond and promote efforts toward controlled engineering of optical centers in fluorescent diamond particles.

Micro-scale abrasion investigations of single-crystal diamonds using nano-polycrystalline diamond wheels

A small grinding wheel of 3.2 mm in diameter was prepared from nano-polycrystalline diamond (NPD) obtained by direct conversion sintering under high pressure and high temperature. Using this NPD wheel as a grinding blade, a new useful method for investigating the micro-scale abrasive properties of single-crystal diamonds was developed. Since NPD has an extremely high hardness of about 130 GPa, the abrasive properties of various natural and synthetic single-crystal diamonds, whose hardness is usually around 70 to 125 GPa, can be appropriately evaluated. In addition, since the wheel diameter is very small, it is possible to measure the abrasion resistance in a minute region of several tens of μm in a diamond crystal. It was confirmed that the method can accurately evaluate the abrasive properties of minute regions of single-crystal diamonds using synthetic type IIa diamond. It was also demonstrated that it is possible to investigate how the abrasive properties of synthetic type Ib and natural type Ia diamonds change depending on the distribution of impurities or crystal defects in the crystals.

Photoluminescence studies of optical centers generated by the B ion irradiation in Ib diamond

The photoluminescence (PL) spectra were employed to study the optical centers generated by the B ion irradiation in Ib diamond. The luminescent spectra with zero phonon lines (ZPLs) centered at 573, 575.8, 637.9, 390.8 nm and the most of the vibronic bands in vicinity of the ZPLs were detected using 532 and 325 nm lasers. The function of spot scan, surface scan and depth scan of Renishaw micro-Raman spectrometers were performed to understand spatial distribution of the resulting high density optical centers at 80 K. Through the spatial distribution of 575.8 and 637.9 nm optical centers, it was found that it’s more advantageous to form 575.8 nm optical centers for high density nitrogen diamond irradiated by B ion and subsequent annealing. Based on the principle of electrical neutrality and the degree of lattice distortion, it was proposed that a possible defect evolution process of the B-related optical center.

Microdiamonds in Alkalic Dolerites from the North China Craton: FTIR and C Isotopic Characteristics

Most of the diamond deposits in China are in the North China Craton. In addition to gem diamonds in kimberlite, a large number of microdiamonds have also been discovered in alkaline dolerites. These microdiamonds show very different characteristics from those recovered in kimberlite. Here, we report the morphology, colour, nitrogen contents, and carbon isotopic compositions of the diamonds recovered from the alkalic dolerites in eastern China. The microdiamonds are mainly cube and rhombic dodecahedron with diameters of 0.2 to 0.6 mm. Infrared spectrum analysis shows that these microdiamonds are mostly type Ib with a small amount of type Ia. The Y centre is obvious in type Ib diamond. Modelling mantle residence times for the IaAB diamonds is about 550 Ma. Nitrogen contents of the diamonds range from 4.5–503 ppm, with a median value of 173 ppm. The total δ13C range of the microdiamonds varies between −18.6 and −21.1‰ and are similar to those of ophiolite diamond.

Mixed type Ib-IIa diamond from a Fe–Mg2Si3O8·5H2O–C system under high pressure and high temperature

The composition of the crystalline medium has an essential effect on the formation and properties of diamonds. Large single-crystal diamonds grown in a Fe–Mg2Si3O8·5H2O–C system by the temperature gradient method (TGM) at 5.8–6.3 GPa and 1400–1480 °C were investigated. It was found that as the Mg2Si3O8·5H2O content increased from 0 to 4 wt%, the synthesis pressure and temperature both increased, and more nitrogen-vacancy (NV) defect centers appeared in the diamond crystal. The nitrogen impurity concentration in type Ib diamonds synthesized in the pure FeC system was about 90 ppm, and the distribution of nitrogen impurities was uniform from core to rim. Furthermore, with a Mg2Si3O8·5H2O content of approximately 4.0 wt%, type Ib-IIa diamond was successfully synthesized. The infrared spectra (IR) results showed that the nitrogen content of the type Ib-IIa diamond was higher in the central zone of the crystal (79 ppm), decreased in the intermediate zone (42 ppm), and decreased further at the periphery (< 1 ppm). Thus, the type Ib-IIa diamond had significant heterogeneity in the distribution of nitrogen.

Vacancy diffusion and nitrogen-vacancy center formation near the diamond surface

For the engineering of nitrogen-vacancy (NV) centers in diamond, vacancies have been introduced locally into a type Ib diamond (100–200 ppm nitrogen content) by implanting argon ions from a sub-500 nm focused beam. At an acceleration potential of 12 kV, different charge states (Ar n+, n={1,4,8,11}) result in kinetic energies of 12–132 keV. NV-centers were formed by a subsequent annealing step. A wide range of fluences from around one ion to several hundred ions was implanted per spot. It was found that, on average, between 0.04 (12 keV) and 0.79 (132 keV) NV-centers are created from the vacancies of a single implanted argon ion, depending on the ion energy, but not on the fluence. The different number of vacancies created at each energy alone cannot account for the difference in NV-center yield. However, the probability of a given vacancy to diffuse to the diamond surface during annealing, where it cannot contribute to NV-center formation, was simulated and can fully explain the NV-yield behavior. With this model, an upper bound of approximately 300 nm for the diffusion length of a single vacancy was found for an annealing temperature of 800 °C.

Temperature dependence of optical centers in Ib diamond characterized by photoluminescence spectra

The optical properties of defects in Ib diamond prepared by Chemical Vapor Deposition (CVD) and High Pressure High Temperature (HPHT) methods are studied by photoluminescence in a temperature range of 77– 297 K. The temperature dependence of color centers in diamond of 2.65 eV center, NV0, NV-, SiV-, 3H is studied. The zero-phonon line (ZPL) shift, intensity and full width at half maxima (FWHM) have a strong temperature dependence. The study shows that, due to the expansion of the lattice and the enhancement of the electron-phonon coupling strength, the ZPL shift can be described by the modified Varshni model which shows great potential in temperature sensing. The FWHM of ZPL matches a cubic function of temperature, this model can be employed to well describe the broadening of ZPLs in the defect-rich diamond. And the thermal quenching of absolute PL intensity can be described by the Arrhenius equation. Meanwhile, the difference of variable PL signal between CVD and HPHT samples is analyzed.